Optical microscopes and their peripheral devices, which contribute to studies in various fields, have been provided with the function of capturing images of, in particular, an observation target object using an image pickup device in recent years. They send out image data of a captured still image or moving image to external devices such as a computer and a large monitor, and are used for image analysis and phenomenon analysis. Further, the automation of the overall function of the optical microscope is also progressing. For example, in order to adjust the optical microscope while analyzing an image obtained with the optical microscope, the positional adjustment of a stage on which the observation target object is placed, and the operation of switching between a plurality of mounted objective lens having different magnifications, can be performed by a remote operation.
For example, in the field of life science studies, time-lapse observation is often performed in which a high-resolution analysis image is observed over a long period of time in order to analyze the change in the microstructure inside a cell, the pattern of cell differentiation, and the like by using a high-resolution optical microscope. An optical microscope has a very narrow focal length because of its high magnification, and the observation target object will be out of a focal position of the objective lens due to a slight vibration or change in the ambient temperature. In addition, in order to observe the above-described structural change inside a cell, it is often the case that a thermal stimulation is applied externally to a cell to be observed. If this causes a change in the ambient temperature, the focus state to the observation target object is impaired, resulting in the problem that changes in the cell structure cannot be observed accurately.
For this reason, optical microscopes equipped with an autofocus device that can automatically maintain the focus state of the objective lens have been developed. As an autofocus device in the field of optical microscopes, an active autofocus method having a high-speed tracking performance is used. This active autofocus method causes autofocus light emitted via an objective lens to be reflected by a reflection film provided on an interface between a slide glass on which an observation target object is placed and a cover glass mounted on the observation target object or by the interface itself, and from the received reflected light, accurately measures the interval between the objective lens and the observation target object, and maintains this interval constant.
In recent years, there have been proposed optical microscopes capable of performing accurate autofocus even in the case where the interface of the slide glass and a cell nucleus serving as the observation target object are at positions having slightly different intervals with the objective lens, including, for example, a case where only a single nucleus in a cell is observed as performed in the field of the studies of life science. For such an optical microscope, there has been proposed a technique by which focusing is achieved at a position shifted by a predetermined amount from a focus position obtained by the active autofocus method, based on data obtained by a focus operation to the slide glass or the like by the active autofocus method and a focus operation performed by the operator to the observation target object by using an observation optical system (See Patent Document 1).
There has also been proposed a technique by which a focus adjustment lens system is included in the autofocus optical system in the active autofocus method, a focus offset amount is set by performing a focus operation by the operator in a state in which an autofocus operation by the active autofocus method has been performed for the slide glass or the like, and afterward, a focus operation by the active autofocus method is performed by the focus adjustment lens while the focus offset amount is maintained (See Patent Document 2).